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Aspirin and Cancer Prevention: What the Research Really Shows

Sep 24, 2015

The U.S. Preventive Services Task Force (USPSTF) last week released draft recommendations around the use of aspirin to help prevent disease, including both cardiovascular disease (heart attacks and strokes) and colorectal cancer. The inclusion of colorectal cancer as part of these guidelines is a first.

The USPSTF is a government appointed, but independent, panel of medical experts whose recommendations are highly influential in guiding what doctors tell their patients to do. The new USPSTF recommendations are still a draft. They are currently open for public comment, and USPSTF will review the feedback it gets before making a final decision.

There are risks and benefits to regular aspirin use, and the USPSTF weighed both in order to come up with their recommendation. The draft guidelines are recommending that certain adults in their 50s, who are at higher risk of a heart attack or stroke, and do not have risk factors for stomach bleeding, start taking low-dose aspirin daily to help prevent cardiovascular disease and colorectal cancer. Regular aspirin use can cause serious health problems such as stomach bleeding, which is why no public health organization, including the American Cancer Society, recommends taking aspirin solely to reduce cancer risk.

In this interview, American Cancer Society researcher, Eric J. Jacobs, Ph.D., provides insights into the draft USPSTF guidelines as well as what studies to date really show when it comes to aspirin and cancer prevention, and discusses what other research is still needed.

Q.What’s new about the draft guidelines that the USPSTF recently put out?

A. The new USPSTF recommendations about aspirin use are based on a comprehensive analysis of both risks and benefits. This analysis weighs the benefits of long-term low-dose aspirin use for preventing both cardiovascular disease (strokes and heart attacks) and colorectal cancer against its risks, which include serious gastrointestinal bleeding. Previously, there were USPSTF recommendations for aspirin use by individuals at high risk of cardiovascular disease, but these did not factor in lowered risk of colorectal cancer.

The change in recommendations by the USPSTF reflects the accumulation of scientific evidence linking aspirin with a lower risk of colorectal cancer. As an American Cancer Society researcher, I’m proud to say that the first major study on aspirin and lower risk of colorectal cancer in humans, published in the New England Journal of Medicine in 1991, was conducted by American Cancer Society epidemiologists using data from the Society’s Cancer Prevention Study II (CPS-II).

Q. Is there, at this point in time, definitive evidence that regular aspirin use may help prevent certain cancers?

A. Yes, there is now definitive evidence that long-term daily aspirin use, even at low doses, will lower risk of developing colorectal cancer, probably by approximately 40%. However, this benefit is unlikely to “kick in” immediately. There appears to be a delay of several years between when aspirin use is started and when risk of developing colorectal cancer is reduced. This delayed preventive effect of aspirin was built into the risk-benefit calculations behind the new USPSTF recommendations.

Q. In addition to colorectal cancer, are there certain types of cancers for which the evidence is stronger?

A. Besides colorectal cancer, there is good evidence that aspirin use lowers the risk of developing cancer of the esophagus, and fairly good evidence that aspirin use also lowers the risk of developing stomach cancer. These two cancers are not among the most common in the U.S., but they are of some importance because they tend to be very hard to treat.

For other cancers, the evidence is weaker. Some studies suggest that aspirin users are at slightly lower risk of developing certain other cancers, including two of the most common, breast cancer and prostate cancer. However, other studies have found no effect. None of these studies are randomized trials, the most reliable type of study, where people are randomly assigned to take either aspirin or a placebo pill.

Q.What other studies need to be done to clarify whether aspirin can play a role in preventing other types of cancer as well. And is it that more studies are needed, or that different types of studies are necessary?

A. The best study would be a new randomized trial where tens of thousands of people would be randomly assigned to take aspirin or a placebo pill daily for at least 10 years. However, a large long-term study like this would be expensive, and no such study has yet been started.

Two types of ongoing studies will help clarify what additional cancers aspirin may help prevent, and how long aspirin needs to be taken before any effects on cancer become apparent. First, there are randomized trials designed to study the effects of aspirin on heart disease – information from these same studies could be analyzed to study its effects on cancer as well. However, these studies may not answer questions about long-term effects because they typically involve taking aspirin for only about 5 years. Second, there are high-quality “observational” studies that track large numbers of people for decades, asking for detailed information on aspirin use every few years. A good example is the American Cancer Society’s recently started Cancer Prevention Study 3 (CPS-3), which includes approximately 300,000 men and women who will be tracked for at least 20 years. Over time, data from CPS-3 and similar studies will help clarify the long-term effects of aspirin on a wide range of cancers and other diseases.

Q.Do you think the research on aspirin and the prevention of other types of cancers is promising – or is it really too early to say?

A. Research on aspirin and cancer prevention is definitely promising. It now appears possible that, over the long term, the same daily low-dose aspirin that can help prevent heart attacks could also help lower risk of several cancers. At the same time, even low-dose aspirin is a real drug, with potentially serious side effects. These include increased risk of ulcers and stomach bleeding, which can occasionally be serious enough to require blood transfusions and even cause death. Aspirin use is not right for everyone.

Q.What is the bottom line at this time when it comes to taking aspirin?

A. Neither the American Cancer Society, nor any other health organization, recommends taking aspirin solely to help prevent cancer. People who are wondering if they should take aspirin should talk to their own health care provider, who knows their individual medical history and is aware of other medications they may be using, and can take this into account when weighing the overall risks and benefits of aspirin use for them.

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